# weight and power

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#### flienlow

##### Active Member
How does weight and power affect an airplane in regards to choosing an engine for a homebuilt AC?
Example, a Lycoming 0-320 is heavier than a Continental O-200, but has more horsepower.
Assuming all conditions are the same and engineering was in place, would you gain a greater useful load out of a higher horsepower engine, or does the higher HP just mean that you would have better climb/cruse performance? I don’t quite understand how that works.

##### Well-Known Member
More power is more climb, more fuel burn and more speed.

Usually more power also means a heavier engine, which eats into your usefull load; you can't take the overweight of the engine as weight in passengers/fuel anymore.

#### Topaz

##### Super Moderator
Staff member
Log Member
In the final analysis, it's the power loading of the aircraft (weight/installed power) that matters in this vein. Power loading affects climb performance, primarily, when combined with other factors such as wing loading, span, overall parasite drag of the aircraft, etc.

The useful load of the airplane is simply the maximum allowable weight of the aircraft in flight (including payload, fuel, oil, etc.), minus the weight of the aircraft alone (the "empty" weight). The maximum weight, usually called the "Gross" weight or "Maximum TakeOff Weight" - MTOW - is usually a limit imposed by the structure of the aircraft. The installed power of the engine therefore doesn't directly affect the useful load of the airplane. The weight of the engine does, however, as it contributes to the overall weight of the aircraft. So the weight of the engine counts towards the empty weight. Obviously an engine that puts out more power for a given weight is more desirable, all else (reliability, cost, etc.) being equal.

During design, you'll figure out a combination of MTOW and power loading that will fit your performance requirements and useful load requirements for your design. In that process, you can either choose a fixed power and determine the airplane that can meet your requirements on that power (limiting range, payload, etc. in order to meet your other goals), or you can choose a set of requirements and payloads, and then size the aircraft from that, without specifying a particular installed power, and when everything lines up, you then know how big an engine you need. There are structured methods of doing this, which fall under the category of "Sizing". Aircraft Design: A Conceptual Approach by Dan Raymer is rather the "bible" on this subject, along with other aspects of "conceptual" early-phase aircraft design. If you just want a primer or overview of the process, before springing for the entire "big" book, Raymer has a book called Simplified Aircraft Design for Homebuilders, that introduces the sizing in a more limited way. The smaller book is a good start, but the larger ... A Conceptual Approach is really necessary if you're going to really design a full-sized airplane.

#### Dana

##### Super Moderator
Staff member
Like everything in aviation, it depends.

If the gross weight is structure limited, then installing a bigger engine would only decrease useful load, since you can't increase the gross weight. Generally, this is the case, since a designer will try to make the structure as strong as it needs to be, but not any stronger (since that adds weight). OTOH, if you have an overly strong airframe but the gross weight is limited by climb performance due to an underpowered engine, then a bigger engine would help... as long as the weight increase from the bigger engine doesn't negate the gains.

Speed gains from adding power are generally very small... and the higher fuel consumption means more fuel which means less cargo, etc...

-Dana

Do YOU trust a government that won't obey it's OWN LAWS?

#### wsimpso1

##### Super Moderator
Staff member
Log Member
+1 on Dana and Topaz

#### Battson

##### Well-Known Member
The answer is YES - if the engineering is in place either way - the bigger engine means more performance. You want to think about power loading (power per weight) as defining performance, rate of climb, takeoff distance, maximum cruise speed (forget fuel economy), service ceiling, that kind of thing.
Make an air cooled piston engine bigger and it typically gains more power than more weight (through the "normal aircraft range" to a point about 400hp). Ergo if you want more performance, you need to lose weight or add power (if your structure can take it)..

About weight... Conversations on a similar subject on another forum are suggesting that most aircraft's MCTOW is normally limited by the C for certification.
As you add more weight the climb performance becomes too poor, stall speed too high, prop noise too loud, undercarriage movement too restricted, etc rather than the physical structure of the wing or fuselage being unable to support the weight increase.

Thank you all!

#### Armilite

##### Well-Known Member
More power is more climb, more fuel burn and more speed.

Usually more power also means a heavier engine, which eats into your usefull load; you can't take the overweight of the engine as weight in passengers/fuel anymore.
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Maybe in Certified Aircraft Engines that's True, but in 2 Strokes, not neccessarly true. A 582UL (65hp at 6500rpms), and a Skidoo/Rotax 670 Conversion (92hp at 6500rpms) there is only about a 8 lb difference, vs a 27hp difference. At the same Cruise rpms, a 670 gets 1 GPH better than the 582UL, account it use's RAVE Vales, like the 618UL did.

#### BJC

##### Well-Known Member
HBA Supporter
More power is more climb, more fuel burn and more speed.

Usually more power also means a heavier engine, which eats into your usefull load; you can't take the overweight of the engine as weight in passengers/fuel anymore.

See Avitar: This design is one of the most efficient that there is in terms of aerobatic performance per cost.
(800 pounds empty, 1,100 with me, parachute, and fuel) / (207 HP) = 5.3 lbs/HP of pure fun.

BJC
"You can have too much weight, but you never can have too much power."

#### Armilite

##### Well-Known Member
See Avitar: This design is one of the most efficient that there is in terms of aerobatic performance per cost.
(800 pounds empty, 1,100 with me, parachute, and fuel) / (207 HP) = 5.3 lbs/HP of pure fun.

BJC
"You can have too much weight, but you never can have too much power."
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A 670 with a Turbo with 11lbs of Boost 205.4hp.

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#### dcstrng

##### Well-Known Member
Wow -- and with specific consumption hovering around 0.60, that's impressive...

#### TFF

##### Well-Known Member
Can you make that power for 2000 hrs, 1000? 500? Will it blow up in 100? HP is easy; HP with life is hard, and a prop is very hard on engines. What everyone wants is an engine they can buy and not do anything for 20 years. Hoping to pass the engine rebuild to the new owner before they get caught out.

#### Armilite

##### Well-Known Member
How does weight and power affect an airplane in regards to choosing an engine for a homebuilt AC?
Example, a Lycoming 0-320 is heavier than a Continental O-200, but has more horsepower.
Assuming all conditions are the same and engineering was in place, would you gain a greater useful load out of a higher horsepower engine, or does the higher HP just mean that you would have better climb/cruse performance? I don’t quite understand how that works.
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Your talking only a 50hp difference, a 70lbs weight difference. A new o-200 about $23,000, I don't know if you can even get a new O-320, but it's price would be much higher I'm sure if it's still made. You can rebuild an O-200 with a HP Cam, higher CR Pistons, Electronic Ignition, bigger Intake Valve, a better Tuned Exhaust, Fuel Injection, etc., to save some weight also, and use all the new Engine Coatings available, and make more HP also, probably close to 140-150hp with all the upgrades available. It only takes$.
[h=2]Specifications (O-320-A1A)[/h]Data from TYPE CERTIFICATE DATA SHEET NO. E-274 Revision 20[2]
[h=3]General characteristics[/h]
• Type: Four-cylinder air-cooled horizontally opposed engine
• Bore: 5.125 in (130.18 mm)
• Stroke: 3.875 in (98.43 mm)
• Displacement: 319.8 cu in (5.24 l)
• Dry weight: 244 lb (111 kg)
[h=3]Components[/h]
• Valvetrain: Two overhead valves per cylinder
• Fuel system: Updraft carburetor
• Fuel type: minimum grade of 80/87 avgas
• Oil system: Wet sump
• Cooling system: Air-cooled
[h=3]Performance[/h]
==================================================================
[h=2]Specifications (O-200-A)[/h]Data from Engine specifications: O-200-A & B.[22]
[h=3]General characteristics[/h]
• Type: Four-cylinder air-cooled horizontally opposed piston engine
• Bore: 4.06 in (103.1 mm)
• Stroke: 3.88 in (98.6 mm)
• Displacement: 201 in³ (3.29 L)
• Length: 28.53 in (724.7 mm)
• Width: 31.56 in (801.6 mm)
• Height: 23.18 in (588.8 mm)
• Dry weight: 170.18 lb (77.19 kg) dry, without accessories
[h=3]Components[/h]
• Valvetrain: Hydraulic lifters, two pushrod-actuated valves—one intake, one exhaust—per cylinder
• Fuel system: Updraft carburetor with manual mixture control
• Fuel type: 80/87 avgas minimum
• Oil system: 6 US quart (5.7 L), wet sump
• Cooling system: Air-cooled
[h=3]Performance[/h]

HBA Supporter

#### Pops

##### Well-Known Member
HBA Supporter
Log Member
Power --- Good
Should I install a bigger engine--- Depends.
Next question.
Dan

#### mohawker2000

##### Member
Where would I find information on replacing Mags with Electronic ignition

#### Armilite

##### Well-Known Member
O-320 clone available here: 320 Engine

BJC
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Now that's a decent price for a new 150-160hp engine. A 115hp Rotax is like $35,000. [h=1]320 Engine[/h] [h=4]All New Aero Sport Power Engines Include the Following at No Additional Charge:[/h][h=4] [/h] • Balancing of all rotating and reciprocating components to ensure reduced vibration. • Combustion chamber volume equalization to confirm uniform compression ratios between all cylinders ensuring smooth operation. • Full detailing of all engine components including additional quality control measures i.e. Magnetic Particle Inspection of steel parts, Fluorescent Penetrant Inspection of non-ferrous components and hardness testing of specific components to verify quality. • Painting and detailing to customer specifications. • An Experimental Builder friendly three year parts and labour warranty (engine and accessories) which starts at first flight. • Full Factory support accessible by telephone and email. Includes: • Inhibiting for storage • Logbook, Run-up Sheet, Parts List, Service Bulletin and Airworthiness Directive list Additional Charges: • Engines are subject to a$125 crating charge
• Brokerage and freight charges
[h=3]
New O-320 Aero Sport Power Engines Include:
[/h]Cylinders, Slick Magnetos and Harness, Spark Plugs, Light Weight Starter, Carburetor, Fuel Pump, Flat Tappet Camshaft or Roller Lifter Camshaft, Oil Sump, Connecting Rods, Balanced Hollow Crankshaft, Conical or Dynafocal Type 1 Crankcase, Ring Gear, Inner-Cylinder Baffles, Spin On Oil Filter Adapter, Vacuum Pump Adapter Housing, Dipstick and Tube.Fixed pitch (D2A) or Constant speed (D1A) 150 HP or 160 HP
 Fixed Pitch (D2A) Outright with ECI Components $25,700 US with Superior Roller Lifter Technology$27,100 US Constant Speed (D1A) Outright with ECI Components $25,900 US with Superior Roller Lifter Technology$27,300 US

[h=3]New IO-320 Aero Sport Power Engines Include:[/h]Cylinders, Slick Magnetos and Harness, Spark Plugs, Light Weight Starter, Precision Silver Hawk Fuel Injection, Fuel Pump, Flat Tappet Camshaft or Roller Lifter Camshaft, Oil Sump, Connecting Rods, Balanced Crankshaft, Concial or Dynafocal Type 1 Crankcase, Ring Gear, Inner-Cylinder Baffles, Spin On Oil Filter Adapter, Vacuum Pump Adapter Housing, Dipstick and Tube.

Fixed Pitch (D2A) or Constant Speed (D1A) 150 HP or 160 HP

 Fixed Pitch (D2A) Outright with ECI Components $27,700 US with Superior Roller Lifter Technology$29,100 US Constant Speed (D1A) Outright with ECI Components $27,900 US with Superior Roller Lifter Technology$29,300 US

#### Armilite

##### Well-Known Member
Can you make that power for 2000 hrs, 1000? 500? Will it blow up in 100? HP is easy; HP with life is hard, and a prop is very hard on engines. What everyone wants is an engine they can buy and not do anything for 20 years. Hoping to pass the engine rebuild to the new owner before they get caught out.
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What do you expect out of a $4500 engine, a free trip also to the moon? There isn't many Certified Engines that make that 20 years/2000hr TBO, and not do anything to it. Hirth has a 1000hr tbo on all of it's 2 Stroke engines at 75% Power. Simonini has a 600hr tbo on all of it's 2 Stroke engines. Rotax has a 300hr tbo on all of it's 2 Stroke engines, even though many people run them 500-700hrs before they rebuild them. There are a few 582, and 503s with over 1300hrs on them and still flying. Good Engine Maintenace & Care, has a lot to do with how long they all last. A Rotax Rick, 92hp 670(450hr tbo) 2 Stroke, cost about 1/4 of a comparable 100hp 4 Stroke like a new O-200(2000hr tbo). To rebuild that 670 at 450hrs, costs way less than that O-200. Since the USA national flying average is 50hrs a year, that 450hrs is avg. 9 years of flying. A 2000hr tbo would be avg of 40 years of flying. In the long run, you will spend way less, even rebuilding the 2 stroke, unless you can do your own work on the O-200. Your probably talking$2000 for the 2 Stroke rebuild vs $8000-$10,000 for the O-200 rebuild.

If you push any engine over the stock designed HP/RPM Rating, it's service life will probably be shorter, but a lot has to do if it's built right in the first place. None of these Airplane engine companies have taken advantage of new Parts, new Technology, and new Materials, or new Engine Coatings, that has come out in the last 15+ years.

Remember when a Ford, Chevy, Dodge, etc., engine was considered wore out at 100,000 miles, now there just broke in.